Two-stroke internal combustion engines—such as those used in chainsaws, brushcutters, and the like—are often equipped with carburetors for mixing and supplying air and fuel to the engine. Layered scavenging carburetor arrangements having separate air-fuel passages and air passages can be used to reduce, and often prevent, undesirable blow-through and fuel-loss through its exhaust. But sometimes these arrangements generate air and fuel mixtures that are too lean for an idle operating condition or other low speed and low load conditions.